The so called carpenter's square is one of the most complicated of the basic life and death positions. It is said that anyone who completely understands the shape is at least professional shodan. It was misunderstood until the 1300s. It is simple enough as far as its vital point and status are concerned - it almost always results in a ko. However there are endless ways to set up the ko, and even more ways to defend incorrectly and end up dead anyway.

The discussion is divided into an easy part and a difficult part. More discussion is found at the weak carpenter's square.

Difficult part

No outside liberties

Basic ko (no outside liberties)

The best way to set up the ko depends to a large extent on the number of outside liberties of the black group. If Black has none, White starts by playing on the vital point. Black attaches on the first line, and White stretches in the other direction.

Continuation

White further reduces the black eye space and after 5, the only way left for Black to live is engage in a ko.

Throw-in ko

Bill: If , after makes a throw-in ko at a or b. White can also make seki at a.

Book references

Online references

It seems that one as white, one would only need to learn the method that works with 2 outside liberties, as it will also work in 1 and 0 outside liberties. As black, the other variations I suppose have some value in knowing why they don't work (or work as well for white) in the 1 and 2 liberty versions... Or have I missed something?

(Sebastian:) The difference is that the edges have to be better protected. In diagram "Two outside liberties", you need the marked stone . With 0 liberties, you can do without.